DOCSIS is a protocol that is used to send digital video and data between a hub or headend facility (HEF), and a cable modem (CM), gateway, or a set-top box at a customer premise. DOCSIS originates and terminates via a cable modem termination system (CMTS) at one end and a CM at the other end. For downstream and upstream transport, the digital data are modulated onto a Radio Frequency (RF) carrier or channel using Quadrature Amplitude Modulation (QAM) techniques. There are two types of CMTS architectures: 1) a CMTS with an integrated physical (PHY) layer and 2) a CMTS with a distributed PHY, e.g., on a separate PHY shelf collocated with the CMTS or a remote PHY that is further downstream and closer to the customer's end equipment. The CMTS with a distributed architecture is referred to as a modular CMTS (M-CMTS). In this context a PHY refers to the physical modulation and upconverter technology, and is sometimes referred to as a coaxial media converter (CMC) or an optical coaxial unit (OCU).
To facilitate some markets, a third CMTS architecture has been specified by the cable industry's governing body, CableLabs® that supports conventional video in addition to DOCSIS, and is referred to as a Converged Cable Access Platform (CCAP). When the QAM is physically removed from an integrated CMTS and placed downstream it is known as an edge QAM (EQAM) or downstream PHY device. Thus, the CCAP architecture allows DOCSIS and existing video distribution to be combined downstream, thereby allowing network component reuse to reduce overall costs. While providing a more modular architecture, these downstream physical layer devices have a disadvantage in that they each must be manually configured by a network administrator for many of their operating parameters and are not configured with an integrated upstream equivalent of their downstream capability.
For downstream (DS) communication, a downstream protocol has been developed for downstream data transport. The protocol is the Downstream External PHY Interface (DEPI) protocol and is a set of extensions to the Layer 2 Tunneling Protocol version 3 (L2TPv3) protocol that permits an M-CMTS core to connect to and control an EQAM. A standard use of DEPI comprises a Media Access Control (MAC)-to-physical layer (PHY) pair, and has a control connection for managing the DEPI control plane and a unicast data session for transporting downstream data, referred to as a data plane. The payload of the DOCSIS frame within the DEPI data session itself may carry IP unicast or IP multicast traffic for a particular endpoint, however, the control traffic and outer encapsulation of the data traffic is unicast.